The present invention relates to a positioning device incorporating a tool holder for fixing to the end of a robot controlling the displacement of a tool in accordance with a stored path or trajectory.
Whatever task robots have to fulfil, most of them generally serve to make a tool follow a known, stored path, e.g. during a prior learning operation. To this main function is sometimes added the need to carry out a correction of the path followed by the tool during its displacement along the path, in order to take account of certain deformations of the parts, usually resulting from the action of the tool on said parts, or to take account of an incorrect positioning of the parts. Such a correction is performed by a so-called adaptive control process. The deformations can in particular result from the heating of the parts e.g. when the robot used is for welding two parts, or from a mechanical deformation thereof, when it e.g. relates to a cutting or deburring robot.
In practice, the robot is responsible for following the stored path, whereas the path corrections are generally brought about by acting on a tool holder having a certain number of degrees of freedom and which is fixed to the end of the robot. The present invention is independent of the type of robot used and essentially relates to the device used for performing the path corrections.
According to the state of the art, there are a certain number of devices able to fulfil this function. In order to illustrate existing devices, reference is made to French Patent Application No. 80 03152, filed on Feb. 13, 1980 by the Commissariat a l'Energie Atomique. This document particularly shows that such a device must be able to simultaneously support the tool and a detection system generally positioned upstream thereof with respect to the path to be followed. No matter what the detection principle used (mechanical sensor, eddy current matrix-type or unitary transducer, laser scanning optical transducer, etc.), the detection system has to indicate the displacement of the tool relative to the surface discontinuity or break or a profile to be followed and optionally the heightwise displacement of the tool relative to a surface, in order to make the tool correct its path.
A positioning device of this type having a simpler construction is described in the article "A device for guiding the electrode around a curvilinear butt joint during arc welding" by E. A. GLADKOV et ak, pp. 60-62 of the journal Automatic Welding, vol. 26, no. 9, September 1973 (Cambridge, G. B.).
In order to take account of the construction-based displacement existing between the detection system and the tool, in positioning devices of this type the detection system has a certain number of degrees of freedom, independently of the tool. Thus, the signals supplied by the detection system make it possible, by means of an appropriate feedback or control circuit, to position said system above the true path to be followed. A more or less complex and approximate calculation then makes it possible to reset the tool on said path, on the basis of signals emitted by the detection system.
The existing positioning devices of this type consequently suffer from the disadvantage of having a large, complex, heavy and therefore expensive mechanical structure (independent degrees of freedom for the detection system and for the tool) associated with an also complex and costly control electronics (calculation taking account of a time lag linked with the displacement between the tool and the detection system).